1. Field of the Invention
The t invention relates generally to an apparatus and method for computing a position of a moving entity, and more particularly to an apparatus and method for setting a gyroscope zero point or a gyroscope zero point reference value.
2. Description of the Related Art
Telematics terminals mounted in vehicles provide drivers with various information associated with traffic guidance, current events, finance, etc. Many telematics terminals use a global positioning system (GPS) and/or a dead reckoning (DR) sensor to compute a vehicle's position. The DR sensor can use a distance sensor capable of measuring a traveling distance and a direction sensor capable of measuring a traveling angle. The direction sensor can use a gyroscope.
A zero point bias must be accurately measured such that the displacement of a direction angle can be correctly computed. The zero point bias is referred to as the zero point, and varies according to the type of gyroscope or installation environment. In practice, when the gyroscope zero point is measured, vibration is a serious problem. Accordingly, when the gyroscope zero point is measured, a technique robust to vibration is very important.
FIG. 1 is a block diagram illustrating a conventional apparatus for setting the gyroscope zero point.
The conventional apparatus for setting the gyroscope zero point includes a gyroscope 101 for outputting a signal of angular velocity in the form of voltage, an analog-to-digital (A/D) converter 102 for converting the voltage output from the gyroscope 101, and a controller 103 for processing the A/D converted gyroscope output. The controller 103 can be implemented by a microprocessor. The vibration component Vstop that is typically relevant to a vehicle-mounted gyroscope when the vehicle is stopped is defined in Equation 1 below.Vstop=Vb+εthermal—noise+εvibration   Equation (1)
Where, Vb is a true gyroscope bias component, εthermal—noise is a thermal noise component representing a noise level of a gyroscope zero point output measured in a non-vibration and non-rotation state, and εvibration is a component due to vehicle vibration. Accordingly, when a vehicle is stopped, a Vb value is determined by the magnitude of εvibration. In this case, εthermal—noise almost has no deviation between gyroscopes, but εvibration has a significant deviation according to the kind of vehicle in which the gyroscope is mounted and/or according to vehicle wear. For example, the magnitude of εvibration in a car in which a gasoline engine is mounted is smaller than that of εvibration in a truck in which a diesel engine is mounted. That is, because the conventional apparatus uses a fixed noise level to set the gyroscope zero point, there is a problem in that the conventional apparatus cannot be applied to all vehicles. Accordingly, a fixed noise level value must be optimized according to the type of vehicle. When the fixed noise level value is determined according to the vehicle model in case of a telematics terminal built in the vehicle as one part of the vehicle when the vehicle is made, the problem can be addressed. However, since an exact determination as to what kind of vehicle an after-market telematics terminal is mounted in cannot be made, the fixed noise level must be set such that it is appropriate to passenger cars, as they comprise the largest number of vehicles on the road.
FIG. 2 is a graph illustrating a state in which the zero point of a gyroscope is set in a gyroscope mounted in a vehicle having a small vibration level.
When a vehicle having a small vibration level, such as a passenger car in which a gyroscope is mounted is stopped (i.e., not moving), the gyroscope zero point can be successfully measured because a gyroscope output range value 302 measured in an initial zero point determination interval 301 is smaller than a fixed noise level value 303.
FIG. 3 is a graph illustrating a state in which the zero point of a gyroscope mounted in a vehicle having a large vibration level.
When a vehicle having a relatively large vibration level such as a diesel truck in which a gyroscope is mounted is stopped (i.e., not moving), the gyroscope zero point cannot be measured because a gyroscope output range value 402 measured in an initial zero point determination interval 401, is larger than a fixed noise level value 403.